Grinding dust resulting from grinding a ferrous metal such as bearing steel or carburized steel is collected in the form of cotton-like (fibrous) agglomerates including: a grinding fluid containing water and oil; abrasive grains and the like. Since the cotton-like agglomerates contain a large quantity of pure iron, a technique for reusing the agglomerates as a steelmaking material has been proposed. Japanese Unexamined Patent Publications No. 2002-129248 and No. 2003-277842, for example, disclose the following technique. According to the method, a briquette for use as a steelmaking material is formed by the steps of: forming a porous mass (a brittle compact) by compression molding the cotton-like agglomerates using a press, the agglomerates having adjusted contents of water and oil; impregnating a solidification agent into the porous mass by dipping the porous mass in an aqueous solution of the solidification agent; and subjecting the porous mass to natural drying (curing).
A batch type and a belt conveyor type are conventionally known as drying equipment for drying the porous mass impregnated with the solidification agent. The batch type equipment is arranged such that a plurality of porous masses is collectively accommodated in a drying furnace. The belt-conveyor type equipment is arranged such that a conveyor is installed in a furnace and the porous masses are dried while the porous masses are carried on the conveyor.
Since the above method of manufacturing the briquettes by natural drying requires an extremely long drying time, an approach has been made to dry the briquettes quickly by using the drying furnace. However, the porous masses formed by compression molding are significantly varied in bulk density. When the masses are dipped in the aqueous solution of solidification agent, therefore, the amounts of water contained in the porous masses are also varied greatly. If the bulk densities of the porous masses vary in the range of 1.5 to 3.5, for example, the moisture content of the porous masses impregnated with the solidification agent vary in the range of 20 to 200 cc. When the porous masses are dried by means of the batch type or the belt-conveyor type drying furnace, the drying time must be set according to a porous mass having the greatest moisture content.
In case where the batch type furnace is used, the degree of drying varies between a surface portion and a core portion of a porous mass. Hence the porous mass is overdried at the surface portion before the porous mass is dried to the core portion. The porous mass generates heat due to iron oxidization, causing troubles such as ignition and strong odors. Furthermore, there is another drawback of great energy loss. In addition, the batch type furnace requires manual labor leading to a low operating efficiency and also takes a substantial length of drying time (e.g., 10 to 20 hours).
In a case where the belt-conveyor type furnace is used, the furnace has large dimensions in order to permit the conveyor to be installed therein and hence, is low in thermal efficiency (suffers a great energy loss). This results in a drawback of low drying efficiency. Furthermore, a detention time of 3 to 6 hours is necessary for the drying furnace to dry the porous masses. This requires a furnace equipped with an extremely long conveyor, so that the equipment is increased in length and installation area (foot-print).
In view of the foregoing, it is an object of the present invention to provide a manufacture method of briquette for use as metal stock and a manufacturing apparatus therefor, the manufacture method which increases the efficiency of drying the porous masses so as to shorten the drying time, and which provides a simplified constitution for reducing the installation area of the apparatus and for reducing the running cost and initial cost therefor.